Python for Entrepreneurs Transcripts
Chapter: Appendix: Python language concepts
Lecture: Concept: for-in
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In Python we have a fantastically simple way
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to work with collections and sequences.
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It's called the "for...in" loop and it looks like this.
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You just say for some variable name in some collection,
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so here we have "for item in items" and that creates the variable called item
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and we are looping over the collection items,
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it just goes through them one at a time, so here it will go through this loop three times,
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first time it will print the item is "cat", the second time it will print the item is "hat"
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and then finally the item is "mat".
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And then it will just keep going, it will break out the loop and continue on.
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Some languages have numerical "for" loops, or things like that,
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in Python there is no numerical "for" loop,
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there is only these for in loops working with iterables and sequences.
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Because you don't have to worry about indexes and checking links
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and possible off-by-one errors, you know,
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is it less than or less than or equal to, it goes in the test in the normal "for" loop.
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This is a very safe and natural way to process a collection.
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Now, there may be times when you actually need the number,
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if you want to say the first item is "cat", the second item is "hat",
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the third item is "mat", this makes it a little bit challenging.
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Technically, you could do it by creating an outside variable, and incrementing,
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but that would not be the proper Pythonic way.
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The Pythonic way is to use this enumerate function, which takes a collection
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and converts it into a sequence of tuples
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where the first element in the tuple is this idx value, that's the index, the number.
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And the second item is the same value that you had above.
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So first time through its index is zero, item is cat;
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second time through, index is one, item is hat, and so on.
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So these are the two primary ways to loop over collections in Python.
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Remember, if you need to get the index back,
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don't sneak some variable in there, just use enumerate.
